So far I'm running the default novau software and have not tried installing the NVIDIA's software via "Additional Software". I have dual-monitor setup and so wanted to know whether there is going to be some noticeable improvement by installing the proprietary software?

Does the nouveau driver work for you with 12.04? What card do you have?
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Matt JoinerJun 8 '12 at 3:26

yes, nouveau has been working well for me for several years now. GeForce 7600 GT. Not sure of the card on my laptop. I do have an older card that has a problem with both nouveau and nvidia drivers =(
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bodhi.zazenJun 8 '12 at 12:20

Under Ubuntu it's surely the easiest option; i have an Nvidia GeForce 7000m and with the latest version of the drivers i can easily switch from the various dual screen options, so i warmly suggest you to use that. If you want open source drivers it's up to you but i'm not sure they're fully compatible with Ubuntu as what i understand.